A new family of epoxy encapsulants has been developed and is the subject of a pending IBM application. These cleavable epoxy compositions are finding use in microelectronic applications in which the ability to rework part-good assemblies is advantageous. Normally, cured epoxy encapsulants are not reworkable because they are intractable thermosets. These new encapsulants are designed to be reworkable by dissolving the encapsulants in special liquid compositions.
In order to use these new reworkable epoxy encapsulants, an appropriate process needs to be developed for actually removing the encapsulant. The available methods for applying the liquid compositions are immersing the assembly to be reworked in a container containing the heated liquid; directing a spray of the heated liquid at the microelectronic assembly; or applying a small amount of the liquid on a brush and applying the brush to the assembly, while heating the latter on a hot stage. Each of these methods have disadvantages. Immersion of the assembly exposes the whole assembly to the liquid although usually only one part of the assembly needs to be reworked. A directed spray requires tooling to supply the liquid to a spray fixture which has to be designed specifically to contain the spray at the appropriate site of each microelectronic assembly to be reworked. The brushing action can be abrasive to solder mask materials at or adjacent to the site being reworked, and the amount of liquid carried by the brush is limited which slows the rework process.